MAGEST is a database for maternal gene expression information for an ascidian, Halocynthia roretzi. The ascidian has become an animal model in developmental biological research because it shows a simple developmental process, and belongs to one of the chordate groups. Various data are deposited into the MAGEST database, e.g. the 3''- and 5''-tag sequences from the fertilized egg cDNA library, the results of similarity searches against GenBank and the expression data from whole mount in situ hybridization. This database supplies data of DNA sequences and expression patterns of ESTs (Expressed Sequence Tags) from maternal mRNAs of the ascidian egg. We constructed an arrayed cDNA library from uncleaved fertilized eggs of Halocynthia roretzi (Urochordata, Ascidiacea). Both termini of many cDNA clones were sequenced, and whole-mount in situ hybridization to the staged embryos was carried out to obtain information about localization and/or expression sites of the clones. In the phylum Chordata, a genome duplication event took place twice in the process of vertebrate evolution. Ascidian, which is lower chordata, however, has a non-duplicated genome that can be regarded as a basic set of chordate-type genome. This suggests that ascidian is a good model system to investigate functions of genomes of chodates, especially when considering that functional analysis of genes is easily accessible by gene introduction to the ascidian eggs. Fertilized eggs cleave many times to give rise to multicellular organisms. Within embryos, embryonic blastomeres develop into various types of tissues such as epidermis, muscles and nervous systems. In the processes of early embryogenesis, maternal factors stored in the egg cytoplasms are known to play various significant roles. But the functions of the maternal factors in chordate eggs remain elusive compared with those of fruitfly and nematode. Since the last century, ascidian egg has been well known as a mosaic egg in which many blastomeres in the early embryo differentiate autonomously. Recent works have revealed that there exist cytoplasmic determinants that direct formation of epidermis, muscle and endoderm as well as cytolasmic factors involved in axis specification of the embryo and in gastrulation. Thus, various processes of ascidian embryogenesis are mediated by maternal factors in the egg. In this project, we aim at all-inclusive and systematic description of maternal transcripts stored in fertilized eggs of the Japanese ascidian, Halocynthia roretzi; cDNA sequences from ca. 10,000 different genes and their expression patterns during embryogenesis. This will provide an intellectual estate which would allow us to investigate the maternal factors involved in the early developmental events, and consequently, to study the comprehensive maternal genetic information, which can not be achieved by specific investigations on some particular phenonena of embryogenesis. Finally this will also enable us to understand molecular mechanisms of establishment of embryonic body plans of chordates and to understand evolution from invertebrates to vertebrates in future. Sponsors: This work has been supported by a Grant-in Aid from the Ministry of Education, Science, Sports and Culture, Japan (10168213 and 11149212) and by the ''Research for the Future'' Program from the Japan Society for the promotion of Science (96L00404).
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